Rotary kneading screw

Abstract

This invention relates to a rotary kneading screw installed in an extruder kneading and extrusion-molding a material mixture of a synthetic resin such as polyester resin mixed with one or more of master-batch, calcium carbonate, talc and carbon fiber. Progressively higher pressures are applied to the material mixture passing through a kneading section defined in the rotary screw. This rotary kneading screw is thus capable of kneading and extruding the material mixture in a large amount without deteriorating its physical properties and without lowering fluidity and molecular weight thereof even where the material mixture is difficult to knead.

What is claimed is: 
     
       1. A rotary kneading screw structure comprising a shaft having an introductive end and a terminal end; and a plurality of helically disposed flight lands extending radially outward from said shaft and defining therebetween a plurality of kneading recesses, said kneading recesses being of smooth arcuate shape extending in the helical direction with each recess having a deepest part disposed at a middle position of the recess in the helical direction and becoming progressively shallower in depth as it extends away in the helical direction from said deepest part,   said kneading recesses also having the deepest parts of progressively shallower depths from said introductive end to said terminal end,   said kneading screw structure having first channel shaped communicating passages disposed in the axial direction connecting adjacent kneading recesses, said first channel shaped communicating passages having progressively shallower depths from said introductive end to said terminal end,   said flight lands defining second communicating passages disposed between adjacent pairs of kneading recesses, said second communicating passages being defined by a straight line cut through a peripheral segment of the flight lands.   
     
     
       2. A rotary kneading screw structure comprising a shaft having an introductive end and a terminal end; and a plurality of helically disposed flight lands extending radially outward from said shaft and defining therebetween a plurality of kneading recesses, said kneading recesses being of smooth arcuate shape extending in the helical direction with each recess having a deepest part disposed at a middle position of the recess in the helical direction and becoming progressively shallower in depth as it extends away in the helical direction from said deepest part,   said kneading recesses also having the deepest parts of progressively shallower depths from said introductive end to said terminal end,   said kneading screw structure having first channel shaped communicating passages disposed in the axial direction connecting adjacent kneading recesses, said first channel shaped communicating passages having progressively shallower depths from said introductive end to said terminal end,   said flight lands defining second communicating passages disposed between adjacent pairs of kneading recesses, said second communicating passages being defined by a straight line cut through a peripheral segment of the flight lands,   said kneading recess closest to said terminal end having a flow stopping portion extending between two adjacent flight lands and being of the same as the two adjacent flight lands and located at about the same area axially relative to said closest kneading recess as said first communicating passages are located in the other kneading recesses.